


Grown Up Things

by anysin



Category: Gravity Falls
Genre: Bill Is Just A Spirit, Demonic Possession, F/M, Non-Consensual Somnophilia, Older Dipper Pines, Older Mabel Pines, Other, Sibling Incest, Threesome - F/M/M
Language: English
Status: Completed
Published: 2018-10-11
Updated: 2018-10-11
Packaged: 2019-07-29 13:02:30
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 1
Words: 1,359
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16264745
Author URL: https://archiveofourown.org/users/anysin/pseuds/anysin
Summary: Years after Weirdmageddon, Bill punishes Dipper and Mabel for getting over him.





	Grown Up Things

It hurts Bill, that Dipper and Mabel have dared to get over him.

It has taken him a few years, but he’s finally back in Gravity Falls. Unfortunately, he doesn’t have his body anymore - not that it was useful, being stone and all - but he’s hoping to get a new one eventually. For now, he is his old self, a shadow during daytime, a monster in dreams.

He is planning to haunt lots of dreams.

For now, however, he is focused on Dipper and Mabel. They have arrived to Gravity Falls to visit Question Mark and his woman; the Stans are away on an adventure. To Bill’s relief, they don’t stay at the Shack but check in at a motel in the town itself, giving Bill a chance to approach them.

He does so late at night when they’re both in their beds, still chattering to each other. They both seem to be in good health; they are still the same height, both of them just taller now, their bodies still on the slim side. Mabel’s hair is still long, Dipper’s still wild; it’s kind of weird how they both look just the same and so different at the same time. At least their voices have grown noticeably older, Mabel having lost her sweetness while Dipper’s voice has become scratchier.

 _Taking after Grunkle Stan already, eh?_  Bill seethes at the memory of the old man, but he pushes it aside for now; he’ll make the Stans suffer later. Tonight, he is here to enjoy himself, remind both Pine Tree and Shooting Star who holds their respective leashes.

Mabel doesn’t remember, but back when she had been a captive in Bill’s magical bubble, Bill had played around in her brain, creating pathways for himself that he could use to enter her mind whenever he wished. Those pathways are still there, his to exploit.

He waits for the chattering between the two to calm down, for Dipper to fall asleep and Mabel to almost do the same. As Mabel lingers at the edge of dreams, Bill slips inside her, melding into her like he’s a long-missing piece from the puzzle of her body.

All she can do is whimper before Bill opens his eyes in her body.

He sits up in the bed, squinting a bit as he looks around the room; Shooting Star should get her vision checked. Soon, however, Bill is getting out of the bed, keeping his eyes on Pine Tree’s sleeping figure as he reaches or the hem of Mabel’s nightshirt, starting to lift it up.

Neither of the twins are very tall, so Mabel too is still short and petite; Bill lets his hands brush over her small breasts, feeling their soft curves and resting his palms against her hard little nipples for a moment before moving them down. Mabel is already a little aroused, her underwear slightly damp from the crotch when Bill leans down to remove them. It makes Bill smile; so Shooting Star had been secretly getting herself off while she had talked to her brother. Looks like Bill isn’t the only one with longings.

It’s time to see id Dipper feels the same way.

Dipper’s covers are halfway up on his body, the edge of the fabric cutting over his flat, taut stomach. So, Pine Tree works out these days! Bill reaches out to move the covers aside, gaze sliding over Dipper’s taller - he was so small back when they first met, him and Bill - yet still slim figure. Dipper is soft in his grey briefs, but the bulge of his crotch is prominent enough to make it clear to Bill that he isn’t the young boy he knew anymore. They’re both all grown up. Isn’t it time they do adult things together?

Bill climbs up on the bed, moving over to loom over Dipper on his hands and knees. He lowers his body down, ass settling firmly into Dipper’s lap; he rests their thighs together, cradles Dipper’s face between his hands as he leans down.

“I’ve missed you,” he whispers in Mabel’s voice.

If Pine Tree woke up right now, finding his sister straddling him like this, it would be good enough for Bill. However, Dipper isn’t waking up; Bill can cup his face with both hands in peace, turn it to the sides a bit so he can check how far on his face Dipper’s stubble grows, how his features look like now that the baby fat has faded from them. After a while, Bill leans own further, sliding his mouth over Dipper’s.

Shooting Star’s clit twitches between her thighs, which is delightful. What is even more delightful is the slight stirring he senses from Dipper’s crotch, how his soft cocks gets just a little firmer.

Bill wants to laugh, but he doesn’t. Instead, he starts to roll his hips slowly against Dipper’s, rubbing Mabel’s bare, slick crotch against Dipper’s budding erection. Bill swallows a moan as Mabel’s body starts to light up with desire, growing wetter and damper in the groin area while Dipper’s cock swells within his briefs, soon straining against the soft material of the cloth. Bill loves the slight friction of fabric against Mabel’s naked bits, how Mabel’s wetness soaks into it.

He wonders if Mabel has ever thought about it, having Dipper inside her, if Dipper has ever thought about being inside Mabel, He wonders whether they would be shy and tender with each other or go wild like animals, whether they’d be willing to do it in front of Bill.

Those thoughts fill Bill with heat; he utters a soft cry, pressing his face into the crook of Dipper’s neck, holding onto Dipper’s shoulder with one hand while he dips the other between the bodies of the twins, sliding it down to their groins.

“Dipper,” he breathes, closing his fingers around Dipper’s hot, pulsing shaft through his briefs, thrusting Mabel’s groin against the side of her own hand.

Pine Tree groans, cock twitching away as it spills its seed into his briefs.

Bill leaves Mabel’s body then, leaves her on top of her brother’s body with her hand on his crotch, squeezing his covered cock. She gasps when her eyes flow open, hips continuing to rut forward as she comes against her hand, biting down on her lip as she tries to keep herself from making noise. Her shoulders fall slack, but she doesn’t allow herself to fall on top of Dipper, moving hastily away as she scatters off the bed, stumbling her way fast to her own.

Once she’s safe between her covers, Mabel pushes her hand between her thighs, squeezing her legs tight around it while Dipper groans again over in his bed, peeling one eye open as he glares down at himself, at his crotch.

“Wha-?”

He says nothing more, face going red instead when he realizes what must have happened; he must have had a dirty dream right in the same room with his sister. Without even stopping to think about it, Dipper grabs his covers and pulls them all the way up to his neck, breathing hard and fast as he too pushes his hand between his legs, feeling his still throbbing cock and balls up through his briefs.

“Mabel?” he whispers into the darkness.

Shooting Star says nothing, keeping her back turned to Dipper and her hand between her legs as she pretends to sleep.

A shadow again, Bill observes it all, watching as both of them try to calm down and fail, Dipper continuing to stare at the ceiling while Mabel squeezes her eyes shut, desperately trying to cool her excited body down. It takes them a while to start falling asleep again, stop touching themselves.

Bill can’t help but notice that neither of them really finds it unusual to be aroused around the other.

He cackles, freely now that he knows he won’t be heard. This is definitely something he’s going to take advantage of in the future, to make sure both twins know there is no escaping him. But for now, Bill is merciful; he leaves them in peace for the rest of the night.


End file.
